1. Technical Field of the Invention
This invention relates to valves made of carbon fiber reinforced carbon composite materials, for use in internal combustion engines and the like.
2. Description of the Related Art
Current internal combustion engine valves are made from steel and other metals. Most are cast or forged, while some are machined from billets of metal. Metallic valves are heavy and have poor structural properties at higher temperatures. Due to their weight, metallic valves acquire substantial inertia as engine speed (revolutions per minute or "RPM") increases and overwhelm's the valve spring's capabilities, thus limiting the engine's ability to reach higher RPM where more power can be produced. The high levels of friction resulting from conventional steel valve trains also adversely limits engine speed. Furthermore, the temperature restrictions inherent in metallic valves limit engine efficiencies and emissions reductions possible at higher temperatures. These combustion efficiencies and emissions could be improved if exhaust gas temperatures could be raised beyond the current 1500 to 1750 degree Fahrenheit limit of metallic valves. In summary, power losses due to valve spring load and valve-train friction, and inefficiencies and emissions due to exhaust valve temperature limitations, could be significantly reduced if valves were lighter and able to operate at higher temperatures.
Engineers have devoted considerable thought to the goal of finding valve materials that are light and capable of operating reliably at very high temperatures. One such material is titanium, which has long been used to make valves for racing engines. Titanium valves are about half the weight of steel valves and are capable of operating at higher temperatures. However, the high cost of titanium valves make them unsuitable for wider use. A newly devised valve material, titanium aluminide, has shown promise. Titanium aluminide valves are even lighter than current titanium valves and may have some of their high temperature abilities as well. But as with titanium valves, the titanium aluminide material is expensive and the process used to make valves from it is cumbersome.
A non-metallic material proposed for valves is ceramics. Ceramics can be lighter than metals and can operate at higher temperatures. However, ceramic valves presented thus far have been brittle, subject to thermal shock, and prone to catastrophic failure. A prior invention, U.S. Pat. No. 4,928,645, "Ceramic Composite Valve for Internal Combustion Engines and the Like", consists of a fiber reinforced ceramic material designed to counteract the brittleness characteristic of high temperature ceramics. This design shows a carbon fiber reinforcing woven sleeve over unidirectional carbon fiber tows forming a valve stem, onto which a ceramic valve head, containing discontinuous fibers, is molded. This design does not show continuous fibers forming the valve stem and the valve head, but teaches a valve formed of two parts: (1) a stem formed of continuous fibers, and (2) a head formed of ceramic material and containing discontinuous fibers and molded onto the stem. This design is inherently weak and, in practice, prone to catastrophic failure, owing to the lack of continuous fibers throughout the valve, from the stem to the head. Also, because the valve uses both continuous and discontinuous fibers, it is difficult to manufacture. Moreover, so far, the use of ceramic valve materials has not proven successful in internal combustion engines.
The advantage of the presently disclosed invention is that carbon fibers are continuous throughout the valve, forming both the stem and the head in one continuous piece, making it stronger and stiffer and less prone to catastrophic failure. Moreover, since the disclosed invention is formed from continuous fibers throughout, it may be manufactured in quantity more easily. Finally, the disclosed invention is lighter, stronger, and can operate under higher temperatures than prior art valves.